SM5879 datasheet(17/20 Pages) NPC

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SM5879AV

NIPPON PRECISION CIRCUITS—17

Attenuation

The SM5879AV loads the attenuation factor with

serial data by means of the microcontroller interface,

thus enabling attenuation operation.

The attenuation computation is performed by multi-

plying the output of the internal 7-bit UP/DOWN

counter output data by the signal data. When the con-

tents of the counter are DATT, gain can be expressed

by the following equations.

L channel

R channel

When DATT = 0, this becomes -

∞.

When the attenuation factor is changed, it is

smoothly changed from the previous setting until it

reaches the value of the new setting as expressed by

the above equations. The time required to change

gain is approximately 1024 fs

≈ 23.2 msec when the

time required to change one step of the attenuation

factor is approximately 8 / fs

≈ 181.4 µsec over the

range 0 dB to -

∞.

Figure 7. Method of setting the attenuation factor

MLEN

MCK

MDT

(LSB)

(MSB)

Gain

DATT

127

----------------





log

[dB]

Gain

DATT

127

----------------





log

[dB]

Figure 8. Example of attenuation gain

Setting1

Setting2

Setting3

Setting5

Time

Setting4

(Gain)

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